hdparm -T is timing the reading of the disk cache in system memory not out of the hard disks cache so the size of the hard disk cache is irrelevant. This is why people are getting around 1GB/s, if it was pulling it out of the hard disk cache then you'd be maxing out your interface speed of 100-150MB/s for most people.

Also I think the hard disk cache is invisible to the system anyways and therefore unreadable directly.

And that's all she wrote. That's the best that I see. I've played with a few other options, but that's about all I get. I discovered it was running in 16-bit mode, and that helped it get to where it was, along with upping the read-ahead to 15 from 8, but since then, 25/26 seems to be the limit. Not bad, for a laptop, I guess, but I really wanted to see more.

Many posts here is like "look how big my d**k is" so i really need to show u guys mine I have cheap hitachi/ibm disks with only 2 mb cachememory, im surprised to see that they beats much newer and more expensive disks.

So, what, exactly, ARE the bottlenecks that we can run into, and what are the workarounds?

1) Disk's own read-rate. Obviously, we can't read from disk any faster than it can read from the platters, so the max sequential read throughput of the disk is going to be a bottleneck for disk reads. This can be worked around with faster drives, but that's about it.

2) HD to controller. Next up seems to be maxing out the interface itself, (ata66/100/133, SATA150, etc.). That's a hard-limit, but can be worked around with RAID systems, or upgrading the MB/adapter cards/drives/cables.

3) The MB's own transfer rates between the controller and the processor. This is where it starts to get tricky. For a controller in the Southbridge, this is dictated by the chipset, and should be much, much, much higher than any of the others. However, if you've got a PCI-based controller, then the bottleneck is the PCI subsystem. And that's 33Mhz at 16 bits? or what, exactly?

From the reading on this thread, the best the hdparm can do is get the I/O subsystem running such that the bottleneck isn't the software, and how the data is being read, but instead removes all but the hardware bottlenecks that I've described above.

I can't seem to get more than 24MB/sec on my laptop. This being a P4m, with an i845 chipset, the bottleneck is most likely the drive (ATA100/udma5), and not anything else. It's a 5400rpm drive, but the heads are slow, so seeks are horridly slow (24ms), but the sequential read-rate also seems limited.

Those of you seeing much higher transfer rates, I'm guessing that you've got the SATA or udma6, and have drives that can take better advantage of those supporting systems. However, it seems like bothering with the high-speed interfaces when the drives themselves can't push the data is a little useless.

SCSI is different, where you've got multiple drives on the chain, and needing 3 drives to max out the chain actually makes RAID give some BIG performance boosts (ie, RAID0 across three drives could potentially give you full SCSI saturation, and 160MB/320MB transfer rates).

I guess it depends on the cache, doesn't it? I've got a 16MB cache, so if you're doing burst reads, you get full saturation of the pipe, but if doing large sequential reads, you can't saturate the pipe because the drive can't read the data off fast enough.

And then comes the question, what are you trying to optimize for... And that's a whole 'nother ball of wax.

are you serious ?? on a notebook system ?
i have never heard of a harddisks cache that
big not even on desktop hdds and you're talking
about a notebook harddrive ??
is that possible ?

Well, of course it's POSSIBLE, anything like that is. However, it is true. Blew my mind when I found out. I figured that the 8MB on the IBM Travelstars that it's a knockoff of was huge (40GNX?). But it's a great drive, aside from coming from the factory with the write-cache enabled, and XP defaulting to enabled (I find it scary, but no data-loss yet, and everything I do is backed up on servers in CVS).

BTW, it was the supplied drive in my IBM Thinkpad T30. I was definitely amused to find out it was a Toshiba knockoff of the Hitachi/IBM drive...

at wich point does hdparm say your device only supports 8 sectors of filesystem read-ahead ??

i've tried values from 32 - 8192 ( means 16 - 4096 kB )
without hdparm arguing about, but also without any
performance gain.
so far, i do understand that the max value for the -a
parameter could be the complete cache capacity,
that means for our devices a value of
16384, ( 2*8192 ) as they have 8M of cache.

see this excerpt from man hdparm :

Code:

In the current kernel version
(2.0.10) this has a default setting of 8 sectors (4KB).

did you see it talks about 'current' kernel version 2.0.10
and its the most recent version of hdparm ( 5.5 ) i'm using !!

and the difference between -c1 and -c3 is also described in the
hparm man file, it says that they are almost the same, only
that -c3 uses some kind of sync sequence wich is required
for most chipsets, but both of them use 32 bit I/O.

I was about to say that it's rejected past 8, but that was multi-sector reads (-m.

Quote:

i've tried values from 32 - 8192 ( means 16 - 4096 kB )
without hdparm arguing about, but also without any
performance gain.
so far, i do understand that the max value for the -a
parameter could be the complete cache capacity,
that means for our devices a value of
16384, ( 2*8192 ) as they have 8M of cache.

Hmm. worth playing with, but IIRC, I didn't see any performance gains past 15 or so. But in those cases, I *think* I'm running into the limit at which the heads can read the data off the drive. 200-333Mb/sec works out to 25-41MB/sec. However, my Linux partition is at the very end of the disk, where I know the transfer rates aren't as good. So that might be why only 25MB or so on my drive.

now you made me curious, as i own a toshiba notebook
( Satellite Pro 6100) myself.
it uses a hitachi harddrive DK23EA-60
that only has 2M of cache

you are a lucky one ..

EDIT : i just looked your drive up at a local seller,
( because i am now somewhat jealous )
and found out your hdd model ( MK-4026GAX )
is listed for 139.00 euros and another bigger
one ( 80 GB / MK8026GAX ) is available for
279.00.

Perhaps i buy one of these so i can match up with
your specs, just because i'm really jealous right
now...

You must have missed my edit where I added it's an IBM T30. NICE laptop.

EU$130? Not bad. Have to check around here for prices. Want a new drive in the other laptop (9GB, slow, and LOUD). The GAX is silent. audible only when seeking.

UDMA/133 is only going to get better burst rates, any sequential stuff is probably limited by the drive. Lots of smallish reads (ie, fully from the cache) will be faster on UDMA/133, but the drive itself is the bottleneck.

The internal media transfer rate, platter rpm, and seek times are probably MUCH more important than the bus, as a single drive can't suturate the bus.

i.e., my drive is FAST, when it's all out of the cache, but if you need to go to disk, it's SLOW... 25-40MB/sec from the platters, vs. 100MB/sec from disk cache to the host.

woooh.
i just found some review on the t30.
saw it would cost $3,499 ( in june 2002 )
thats pretty much.

but i'm sure its worth it;
as far as i know from friends also owning an ibm
nb, those seem to be perfectly designed.

i paid about 2,400 ? for my Satellite
in jan of last year. it has the pentium-M 2.4
and a geForce 4go, 60 GB harddisk.
but it lacks a touchpad.

i use it mostly for work, that
also explains why it is the fastest system
i own ( my desktop is running 'only' an athlonXP 1900+ )
also its the only system i have running
windows ( 2000 )._________________neoCortex maddin # uname -a
Linux neoCortex 2.6.14-gentoo-r5 #2 SMP Fri Jan 13 04:40:02 CET 2006 x86_64 AMD Athlon(tm) 64 Processor 3400+ AuthenticAMD GNU/Linux

It's a work laptop. Home laptop is a Dell. Not going to buy another Dell laptop. It's WAY too flimsy. IBM laptops are expensive, but good for people who travel on business. They're heavy, but they're solid. I'll take the rigidity and strength of the IBM frames over the flimsy dell ones.